Sharding

Introduction

By default, Playwright runs tests in parallel and strives for optimal utilization of CPU cores on your machine. In order to achieve even greater parallelisation, you can further scale Playwright test execution by running tests on multiple machines simultaneously. We call this mode of operation "sharding".

Sharding tests between multiple machines

To shard the test suite, pass --shard=x/y to the command line. For example, to split the suite into four shards, each running one fourth of the tests:

npx playwright test --shard=1/4
npx playwright test --shard=2/4
npx playwright test --shard=3/4
npx playwright test --shard=4/4

Now, if you run these shards in parallel on different computers, your test suite completes four times faster.

Merging reports from multiple shards

In the previous example, each test shard has its own test report. If you want to have a combined report showing all the test results from all the shards, you can merge them.

Start with adding blob reporter to the config when running on CI:

playwright.config.ts

export default defineConfig({
  testDir: './tests',
  reporter: process.env.CI ? 'blob' : 'html',
});

Blob report contains information about all the tests that were run and their results as well as all test attachments such as traces and screenshot diffs. Blob reports can be merged and converted to any other Playwright report. By default, blob report will be generated into blob-report directory.

To merge reports from multiple shards, put the blob report files into a single directory, for example all-blob-reports. Blob report names contain shard number, so they will not clash.

Afterwards, run npx playwright merge-reports command:

npx playwright merge-reports --reporter html ./all-blob-reports

This will produce a standard HTML report into playwright-report directory.

GitHub Actions example

GitHub Actions supports sharding tests between multiple jobs using the jobs.<job_id>.strategy.matrix option. The matrix option will run a separate job for every possible combination of the provided options.

The following example shows you how to configure a job to run your tests on four machines in parallel and then merge the reports into a single report. Don't forget to add reporter: process.env.CI ? 'blob' : 'html', to your playwright.config.ts file as in the example above.

1. First we add a matrix option to our job configuration with the shardTotal: [4] option containing the total number of shards we want to create and shardIndex: [1, 2, 3, 4] with an array of the shard numbers.
2. Then we run our Playwright tests with the --shard=${{ matrix.shardIndex }}/${{ matrix.shardTotal }} option. This will run our test command for each shard.
3. Finally we upload our blob report to the GitHub Actions Artifacts. This will make the blob report available to other jobs in the workflow.

.github/workflows/playwright.yml

name: Playwright Tests
on:
  push:
    branches: [ main, master ]
  pull_request:
    branches: [ main, master ]
jobs:
  playwright-tests:
    timeout-minutes: 60
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        shardIndex: [1, 2, 3, 4]
        shardTotal: [4]
    steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with:
        node-version: 18
    - name: Install dependencies
      run: npm ci
    - name: Install Playwright browsers
      run: npx playwright install --with-deps

    - name: Run Playwright tests
      run: npx playwright test --shard=${{ matrix.shardIndex }}/${{ matrix.shardTotal }}

    - name: Upload blob report to GitHub Actions Artifacts
      if: ${{ !cancelled() }}
      uses: actions/upload-artifact@v4
      with:
        name: blob-report-${{ matrix.shardIndex }}
        path: blob-report
        retention-days: 1

1. After all shards have completed, you can run a separate job that will merge the reports and produce a combined HTML report. To ensure the execution order, we make the merge-reports job depend on our sharded playwright-tests job by adding needs: [playwright-tests].

.github/workflows/playwright.yml

jobs:
...
  merge-reports:
    # Merge reports after playwright-tests, even if some shards have failed
    if: ${{ !cancelled() }}
    needs: [playwright-tests]

    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - uses: actions/setup-node@v4
      with:
        node-version: 18
    - name: Install dependencies
      run: npm ci

    - name: Download blob reports from GitHub Actions Artifacts
      uses: actions/download-artifact@v4
      with:
        path: all-blob-reports
        pattern: blob-report-*
        merge-multiple: true

    - name: Merge into HTML Report
      run: npx playwright merge-reports --reporter html ./all-blob-reports 

    - name: Upload HTML report
      uses: actions/upload-artifact@v4
      with:
        name: html-report--attempt-${{ github.run_attempt }}
        path: playwright-report
        retention-days: 14

You can now see the reports have been merged and a combined HTML report is available in the GitHub Actions Artifacts tab.

Merge-reports CLI

npx playwright merge-reports path/to/blob-reports-dir reads all blob reports from the passed directory and merges them into a single report.

When merging reports from different OS'es you'll have to provide an explicit merge config to disambiguate which directory should be used as tests root.

Supported options:

• --reporter reporter-to-use

  Which report to produce. Can be multiple reporters separated by comma.

  Example:

  npx playwright merge-reports --reporter=html,github ./blob-reports

• --config path/to/config/file

  Specifies the Playwright configuration file with output reporters. Use this option to pass additional configuration to the output reporter. This configuration file can differ from the one used during the creation of blob reports.

  Example:

  npx playwright merge-reports --config=merge.config.ts ./blob-reports
  merge.config.ts

  export default {
    testDir: 'e2e',
    reporter: [['html', { open: 'never' }]],
  };